Method for producing multi-board electronic device

ABSTRACT

In order to provide an electronic device that has high package density and can facilitate electrical connection between a plurality of circuit boards therein, the electronic device comprises a frame having two mutually opposed openings through major planes, a plurality of circuit boards disposed in the frame parallel to the major plane, and mounted selected electronic circuits thereon respectively, and first and second closure lids for closing the openings in the major plane; the first closure lid contacting with the surface of at least one of the circuit boards, on which no electronic circuit is mounted. Also, on the inner wall of the frame; appropriate stepped portions are formed for supporting the closure lid member, the supporting plate, the circuit board and so forth, Furthermore, in the stepped portion, a portion to accommodate an excess amount of an adhesive is provided.

RELATED APPLICATIONS

This application is a continuation-in-part of Nagasaka et al applicationSer. No. 08/118,785, filed Sep. 10, 1993, now U.S. Pat. No. 5,408,383which was a continuation of application Ser. No. 07/889,701, filed Jun.29, 1992 now abandoned, and claims priority from Japanese patentapplication No. 3-157672 filed May 31, 1991 in Japan, the content of allsaid applications being incorporated hereinto by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an electronic device that canimprove packaging density. More specifically, the invention relates toan electronic device that can improve the efficiency of an electricalconnection between circuit boards and the effect of heat radiation, andprevent adverse effects from heat radiation, in a multi-boardconstruction of the circuit boards. Furthermore, the invention relatesto an electronic device and a lead and a terminal adapted to theelectronic device for facilitating a connection of the boards and a lidmember.

2. Description of the Related Art

In the prior art, there are known electronic devices in which two ormore circuit boards having installed semiconductor integrated circuitsare packed in a single package. (For example, Japanese Unexamined PatentPublication (Kokai) No. 1-147850).

For such devices, various improvements have been made for facilitatingthe wiring between two or more circuit boards. Also, for externalsignalling, lead pins have been employed.

Conventionally, two or more circuit boards forming a multi-boardstructure have been bonded within the package.

In such a construction of the electronic device, the heat generated inthe semiconductor circuits in the circuit board is transmitted to thepackage through the circuit board, or, as an alternative, is radiatedwithin the internal space of the package. Accordingly, heat can beaccumulated within the package that exhibits a low heat radiationeffect.

On the other hand, since the conventional electronic device is designedto establish electrical connection between the circuit boards throughthe lead pins, which are used for externally feeding a signal, whensignals are not commonly output externally, the lead pins have to bedummy pins, thereby resulting in a reduction in the number of activepins for externally outputting the signals.

Also, since the electrical wiring between a plurality of circuit boardsis used in common to the lead pins, the number of connections to beestablished between the circuit boards is limited. In the case of theelectronic device in which the packaging density of the elements isincreased, the amount of wiring for connecting the circuit boardsbecomes large. Therefore, solving this problem is an important task.

In such an electronic device, bonding of the circuit board onto thepackage has been performed without adequate care. Therefore, anexcessive amount of adhesive on the bonding surface may bulge to thesurface of the circuit board, or may drop on the lower circuit board.

Such an excess amount of adhesive can serve to increase the floatingelectrostatic capacity or cause a dielectric breakdown, or can be acause of a failure of electric connection by adhering to the bondingportion on the circuit board. Also, when the adhesive adheres to theconnection lead for an electrical connection between the circuit boards,an abnormal transmission of the bonding power can occur in theconnecting process of the substrate and the connection lead by way ofwire bonding to result in a bonding failure. Furthermore, it is possiblethat the heat radiation effect is lowered because of the adhesive, thuscausing distortion, cracking, degradation of the characteristics owingto a difference in thermal expansion coefficients between the adhesive,the substrate and the connection leads and so forth.

On the other hand, it is typical to coat the upper portion of thecircuit board installing the electronic circuit with a gel form coatingagent for moisture-proofing. In such a case, a coating agent that isinitially in a liquid state, can bulge up along the side wall inside ofthe frame because of surface tension thereof to adhere on the horizontalsurface of the installation guide for the upper circuit board and thuscause a failure of connection between the upper circuit board and theframe. Also, the gel form coating agent can contain foam and thereforedegrade the moisture-proofing effect.

Furthermore, when the coating agent adheres on the connection lead foran electrical connection between the circuit boards, it can cause anelectrical connection failure similar to the adhesive agent.

SUMMARY OF THE INVENTION

In view of the above-mentioned drawbacks in the prior art, it is a firstobject of the present invention to provide an electronic device that canimprove the heat radiation effect of the electronic device packaging aplurality of circuit boards in a multi-board structure.

A second object of the present invention is to provide an electronicdevice that can facilitate electrical connection between the circuitboard in the electronic device installing a plurality of circuit boardsin a multi-board structure.

A third object of the invention is to provide the electronic device thatfacilitates connection of the circuit boards of the electronic deviceinstalling a plurality of circuit boards in the multi-board structure inthe package and prevent harmful effects from the adhesive used in theelectronic device and prevent the occurrence of connection failure.

On the other hand, in the above-mentioned construction of the electronicdevice, in addition to the foregoing drawbacks, there have been manyproblems in the structure of a lead and a terminal. Namely, when thelead and the terminal of the electronic device are connected by way ofelectric welding, the region of the terminal to be welded is formed intoa projection, causing a concentration of the current in the weldingregion. Alternatively, the tip end of the welding electrodes are formedinto an acute angle.

However, in the above-mentioned method, when the projecting portion isplaced in contact with the lead wire, the lead wire slips easily,thereby making it difficult to accurately position the lead wirerelative to the projection on the terminal.

Therefore, a fourth object of the present invention is to provide leadand terminal structures that facilitate positioning of the lead relativeto the terminal and easily produce a concentration of the current.

In order to accomplish the above-mentioned object, an electronic device,according to the present invention, fundamentally comprises:

a frame having two openings through major planes mutually opposed;

a plurality of circuit boards disposed in the frame parallel to themajor plane, and mounting selected electronic circuits thereonrespectively; and

first and second closure lids for closing the openings in the majorplane; the first closure lid contacting the surface of at least one ofthe circuit boards, on which no electronic circuit is mounted.

More practically, the electronic device comprises:

a resin frame having an opening at both end surfaces;

a first metal plate closing one of the openings of the frame;

a first circuit board formed on the surface of the first metal platefacing inside of the frame;

a first electronic circuit mounted on the first circuit board andhandling a relatively large current for generating a relatively largeamount of heat;

a second circuit board arranged at the intermediate position in theframe above the first electronic circuit in parallel relationship to thefirst metal plane;

a second electronic circuit arranged on the second circuit board andhandling less power than the first electronic circuit for generating asmaller amount of heat; and

a closure lid for closing the opening at the opposite side of theopening closed by the first metal plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood from the followingdetailed description and from the accompanying drawings of the preferredembodiment of the invention, which, however, should not be taken topresent the invention, but are for explanation and understanding only.

In the drawings:

FIG. 1 is a section of a practical embodiment of an electronic deviceaccording to the present invention;

FIG. 2 is a perspective view of a frame of the electronic device;

FIG. 3 ms a perspective view of the frame, in which a first circuitboard is mounted;

FIG. 4 is a perspective view of the frame, in which a second circuitboard is mounted;

FIG. 5 is a section showing the construction of the frame;

FIG. 6 is a plan view showing the first circuit board;

FIG. 7 is a plan view showing a flat configuration before bending oflead pins;

FIG. 8 is a perspective view showing a three dimensional configurationafter a bending process of the lead pins of FIG. 7;

FIG. 9 is a plan view showing another flat configuration before bendingof the lead pin;

FIG. 10 is a perspective view showing a three dimensional configurationafter bending the lead pins of FIG. 9;

FIG. 11 is a plan view showing a flat configuration before bending theconnection leads;

FIG. 12 is a perspective view showing a three dimensional configurationafter bending the connection leads of FIG. 11;

FIG. 13 is a plan view showing another flat configuration before bendingthe connection leads;

FIG. 14 is a perspective view showing a three dimensional configurationafter bending the connection leads of FIG. 13;

FIG. 15 is a plan view showing a further flat configuration beforebending the connection lead;

FIG. 16 is a perspective view showing a three dimensional configurationafter bending the connection leads of FIG. 15;

FIG. 17 is a section showing a detailed construction of a first stepportion;

FIGS. 18a and 18b are sections showing the another detailed constructionof the first step portion;

FIG. 19 is a section showing a detailed construction of a third stepportion;

FIG. 20 is a plan view showing a construction of the third step portionmounting the second metal board;

FIG. 21 is a section showing a detailed construction of a fifth stepportion;

FIG. 22 is a section showing a sectional structure of the lead;

FIG. 23 is a back elevation showing the basic side construction of theframe;

FIG. 24 is a section showing the relationship between a die associatedwith a production process of the frame and the connection lead;

FIG. 25 is a perspective view showing a manner for supporting theconnection lead during fabrication of the frame;

FIG. 26 is a perspective exemplary illustration showing inappropriatesupport by an inappropriate configuration of a connection lead duringfabrication of the frame;

FIG. 27 is a perspective view showing the relationship between anotherconfiguration of the connection leads and a manner of supportingtherefor during fabrication of the frame;

FIGS. 28(a)-(c) are cross sectional views showing a connection between aterminal portion of the connection lead and a lead;

FIGS. 29(a)-29(e) are views showing another construction of the terminalportion of the connection lead.

FIG. 30 shows how the gel forming coating agent is injected into theframe 10 and over the first plate;

FIG. 31 shows how the gel forming coating agent is injected into theframe 10 and over the second plate;

FIG. 32 shows one embodiment of the curing process; and

FIG. 33 shows another embodiment of the curing process.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of an electronic device according to thepresent invention will be discussed herebelow in detail with referenceto the accompanying drawings.

In FIG. 1, there is illustrated one example of the basic construction ofthe electronic device according to the present invention. FIG. 2 is aperspective view of a frame 10. FIG. 3 is a perspective view of thedevice, in which a lower first circuit board 50 is mounted on the frame10. FIG. 4 is a perspective view of the device, in which an intermediatesecond circuit board 52 is mounted on the frame 10. FIG. 5 is a sectionof the frame 10.

As shown in FIG. 1, the preferred embodiment of the electronic deviceincludes a frame assembly 1 that defines openings 11 and 12 on majorsurfaces 100 and 200, and a plurality of circuit boards 50 and 52. Onthe circuit boards 50 and 52, any appropriate electronic circuits, suchas a semiconductor integrated circuit or so forth, are mounted. Thecircuit boards 50 and 52 are disposed in the frame in a piling fashionorienting their board surface parallel to the major surfaces 100 and 200of the frame assembly 1. First and second closure lids 40 and 46 areprovided for closing the openings 11 and 12 defined in respective majorsurfaces 100 and 200. At least one of the circuit boards 50 and 52 havea surface on which no electronic circuit is formed; the surface which isplaced in contact with the first closure lid 40. In the shownembodiment, the circuit board 50 is provided with such a surface incontact with the first closure lid 40.

Preferably, the first closure lid, to which the circuit board 50 isconnected by contacting the surface having no electronic circuitthereto, is formed from a metal plate. Another circuit board 52, whichis placed away from the first closure lid 40, also has a surface onwhich no electronic circuit is formed. Such a circuit board surface 52is preferably connected to an appropriate support plate 43. The supportplate 43 is preferably formed from a metal plate.

In the preferred construction, the second closure lid 46 is formed ofthe same metallic material as that of the first closure lid 40.

In the shown construction, the first closure lid 40 serves to radiateheat generated in the electronic circuits on the circuit board 50.

The first aspect of the electronic device according to the presentinvention for achieving the first object of the invention will bediscussed in detail with reference to FIG. 5.

As best shown in FIG. 5, a frame 10 is formed of a synthetic resin intoa parallelepiped configuration. In the shown condition, the frame 10defines an upper opening 12 opening to the external space at the upperside and a lower opening 11 opening to the external space at the lowerside. On the inside surface of the frame 10, a first stepped portion 21,a second stepped portion 22, a third stepped portion 23, a fourthstepped portion 24 and a fifth stepped portion 25 are formed in orderfrom the lower side. Respective stepped portions 21, 22, 23, 24 and 25are defined by horizontal planes 21h, 22h, 23h, 24h and 25h havingnormals oriented in a Y axis direction (vertical axis direction) andvertical planes 21v, 22v, 23v, 24v and 25v having normals oriented in aX axis direction (horizontal axis direction). It should be noted thatthe vertical plane as used in the disclosure is not necessarily limitedto the exactly vertical plane but can include a plane oblique to thevertical or horizontal plane.

As shown in FIG. 6, the first circuit board 50 is fabricated by formingan insulation layer on a metal plate, for example an aluminum plate,which forms first closure lid 40 and forming a circuit pattern on thesurface of the insulation layer. The circuit board integrally formed onthe metal plate 40 is generally called a metal substrate. By bonding theperipheral portion 50a (FIG. 6) of the first circuit board 50 onto thehorizontal plane 21h of the first stepped portion 21, the lower opening11 is closed by the metal plate 40.

It should be noted that the height of the vertical plane 21v of thefirst stepped portion 21 is substantially equal to the thickness of themetal substrate on which the first circuit board 50 is integrally formedso that the bottom of the frame 10 and the back surface 41 of the metalplate 40 lie flush on a common plane.

On the first circuit board 50, a power supply circuit 51 (firstelectronic circuit) composed of power elements, such as power MOStransistor, power transistor and so forth, handling a large current andthus having a large amount of heat generation is mounted, as shown inFIGS. 1 and 3.

As shown in FIG. 1 and 19, the metal support plate 43 is arranged on thethird stepped portion 23. Namely, on the horizontal plane 23h of thethird stepped portion 23, the peripheral portion of the back side 44 ofthe metal support plate 43 is bonded by an adhesive. The second circuitboard 52 is bonded on the surface 45 of the metal support plate 43 bythe adhesive. On the second circuit board 52, a control circuit (secondelectronic circuit) handling a relatively small current and thus havinga relatively small amount of heat generation is mounted. The powersupply circuit 51 and control circuit 53 are coated by silicone gel 16,as shown in FIG. 1. The coating gel material to be employed for coatingthe circuits is not limited to silicon but can be any appropriate resin.

Since such a gel has an adiabatic effect, if the element handling alarge current is mounted on the second circuit board in the foregoingconstruction, the heat generated by such an element may accumulate in aspace defined between the first and second circuit boards 50 and 52 andcannot escape externally. In contrast to this, according to the shownconstruction of the present invention, the heat generated by theelements formed on the first circuit board 50 can be externally radiatedthrough the metal plate 40 having a high heat radiation effect. In theshown construction, since the elements arranged on the second circuitboard 52 will not generate a large amount of heat, no substantial heatwill accumulate within the device.

On the fifth stepped portion 25 of the frame 10, a metal plate (secondclosure lid) 46 is provided for closing the upper opening 12. Namely, onthe horizontal plane 25h of the fifth stepped portion 25, the peripheralportion of the back side 47 of the metal plate 46 is bonded by theadhesive. The surface of the metal plate 46 is exposed to theatmosphere. As set forth above, a casing of the electronic device 1 isformed by the frame 10 and the metal plates 40 and 46.

Since the shown embodiment of the electronic device is provided with themetal plate 40 made of aluminum for closing the lower opening 11 of theresin frame 10, the intermediate metal support plate 43 formed ofaluminum in the frame 10, on which the second circuit board 52 made of aceramic is provided, deflection owing to a difference of the thermalexpansion coefficients between the resin frame 10 and the metal platecan be successfully prevented even at substantially high temperaturessuch as in the engine compartment of an automotive vehicle. Therefore,degradation of reliability because of cracking of the ceramic secondcircuit board 52 or a connection failure at a connecting portion on thesecond circuit board 52 can be successfully avoided. Also, since themetal plate 46 formed of aluminum is provided for the upper ending 12 ofthe frame 10, deflection of the frame and a connection failure of thecircuit board associated with the deflection of the frame can beprevented with greater certainty.

It should be noted that the electronic device illustrated in FIG. 1 ofJapanese Unexamined Patent Publication No. 1-147850 has a resin frameand a metallic closure lid member. The shown construction may causedeflection of the frame owing to a difference in the thermal expansioncoefficient between the resin and the metal thereby causing cracking ofthe ceramic substrate disposed within the frame or degradation ofreliability owing to a failure at the connecting portion.

In contrast to this, according to the shown embodiment, the firstelectronic circuit handling a relatively large current to generate arelatively large amount of heat is mounted on the lower metal plateboard, and the second electronic circuit handling a relatively smallercurrent to generate a small amount of heat is mounted at theintermediate position. Also, the first circuit board is formed on themetal plate closing one opening of the resin frame. Therefore, the largeamount of heat generated by the first electronic circuits is radiatedexternally through the metal plate. On the other hand, since the amountof heat generated by the second electronic circuit is small, sufficientheat radiation effect can be obtained even when the heat is radiatedinternally and by heat radiation to the second circuit board and theframe.

In the above-mentioned embodiment, discussion is provided for theexample, in which two electronic circuit boards are employed. However,the present invention is equally applicable for any multi-boardstructure, such as those employing three or more boards.

Next, discussion will be provided for the second embodiment of theelectronic device suitable for achieving the second object of thepresent invention.

The second embodiment of the electronic device according to the presentinvention has the construction as set out below.

The second embodiment of the electronic device comprises a resin frameforming a casing, first and second circuit boards disposed in a mutuallyparallel relationship within the frame and forming the circuit boards ofthe device, first and second lead pins having a multi pin structureextending from the inside to the outside through the frame and connectedwith the first and second circuit boards at respective inner ends,connecting member maintained at the inside of the side wall of the frameat the side opposite the side where the first and second lead pins arearranged in a stepwise bent fashion, first connecting portion arrangedand exposed to the horizontal surface of the stepped portion formed instepwise fashion at the inside of the side wall of the frame andelectrically connected to the connecting portion of the first circuitboard and second connecting portion arranged and exposed to thehorizontal plane of another stepped portion formed on the side wall andelectrically connected to the connecting portion of the second circuitboard.

In the shown embodiment of the invention, the first and second circuitboards arranged in two stages within the frame are electricallyconnected by the first and second lead pins, through which inputting ofthe external signal and outputting the signal to the external circuitare performed.

On the other hand, in the frame, at the side opposite the side where thefirst and second lead pins are provided, an intermediate connectinglead, bent in a stepwise structure to act as the intermediate connectingmember, is buried. The intermediate connecting member has the firstconnecting portion, the intermediate connecting portion and the secondconnecting portion. The intermediate connecting member is formed insideof the frame to define the stepwise stepped portion. The intermediateconnecting member is so arranged that the horizontal plane of one of thestepped portions is exposed to the first connecting portion and thehorizontal plane of another stepped portion is exposed to the secondconnecting portion. The intermediate connecting member is buried withinthe frame. The second connecting portion establishes an electricalconnection with the connecting portion of the second circuit board.

At one side of the frame and with the intermediate connection lead, i.e.the intermediate connection member buried in the frame, an electricalconnection between the first and second circuit boards can befacilitated.

The practical embodiment of the above-mentioned second embodiment willbe discussed herebelow with reference to FIGS. 7 to 12.

In the frame 10, a connector casing 14 is formed at one side. Within theconnector casing 14, first and second lead pins 60 and 61 are extended.The lead pin 60 is formed by bending the metal plate formed with aplurality of leads in a substantially comb like configuration as shownin FIG. 7, into the configuration as illustrated in FIG. 8. The lead pin60 is buried in the frame 10 by insert molding. As shown in FIG. 1, pins60a are formed at one end of the lead pin 60. The pins 60a extend intothe internal space of the connector casing 14. A bonding portion 60bformed at the other end of the lead pin 60 is provided in the positionexposed on the horizontal surface 22h of the second stepped portion 22.This bonding portion 60b is electrically connected to a bonding portion81 of the wiring pattern in the first circuit board 50 by wire bonding.

Similarly to the lead pin 60, the lead pin 61 is formed by bending themetal plate in the configuration illustrated in FIG. 9 into theconfiguration illustrated in FIG. 10. The lead pin 61 is also buried inthe frame 10 by insert molding. Pins 61a formed at one end of the leadpin 61 extend into the internal space of the connector casing 14. Abonding portion 61b formed at the other end of the lead pin 61 isarranged to be exposed on the horizontal plane 24h of the fourth steppedportion 24. The bonding portion 61b is electrically connected to abonding portion 82 of the wiring pattern on the second circuit board 52by wire bonding.

It should be noted that in the lead pins 60 and 61, frame portions 60cand 61c commonly holding respective leads are separated from each otherby means of a cutter after resin molding so that each of the leads areelectrically insulated from each other.

On the other hand, a connection lead 63 that establishes only electricconnection between the first and second circuit boards 50 and 52 anddoes not have an extending pin for externally feeding signals, is alsoburied in the frame by insert molding. The connection lead 63 is formedby bending the metal plate in the configuration as shown in FIG. 11 intothe configuration as shown in FIG. 12. The connecting lead 63 has abonding portion 63a exposed on the horizontal surface 22h of the secondstepped portion 22 and a bonding portion 63b exposed on the horizontalsurface 24h of the fourth stepped portion 24. The tip end 63c of theconnection lead 63 is bent downward with respect to the frame 10. Frameportions 63d and 63e are bent after resin molding so as to insulate therespective leads to each other. The bonding portion 63a is electricallyconnected to the bonding portion 81 of the wiring pattern on the circuitboard 50 by wire bonding. On the other hand, the bonding portion 63b iselectrically connected to the bonding portion of the wiring pattern ofthe second circuit board 52 by wire bonding. With the connection lead63, electrical connection of part of the wiring of the first and secondcircuit boards 50 and 52 is established.

In the shown embodiment of the electronic device according to theinvention, one example of a process for fabricating the intermediateconnection members 62 to 65 (i.e. connection leads) will be discussedherebelow.

Namely, basically, in the production process of the electronic device asset forth above, when the frame is molded by setting the connection leadas an insert, the connection leads are arranged on the surface thatforms the cavity of the mold. A comb-shaped support plate extendedtoward inside of the cavity from the surface forms the cavity of themold so as to engage with a plurality of metallic leads at the extendedportions. When the connection lead is thus fixed in the cavity, moldingof the frame is performed.

Through the process set forth above, the frame 10 can be molded with thelead pins 60 and 61 and the connection leads 62, 63, 64 and 65 asinserts. As shown in FIG. 24, the mold principally comprises an uppermold 70, a lower mold 71 and a core (not shown). In order to injectmolten resin between the upper and lower molds 70 and 71, a cavity 72 isdefined. The lead pins 60 and 61 and the connection leads 63, 64 and 65are supported on the core for forming the connector casing 14.

On the other hand, the connection lead 62 is arranged in the cavity 72in the following manner. The tip end 62c and the frame portion 62d ofthe connection lead 62 are inserted into a groove 68 defined in thelower mold 71. The frame portion 62e is clamped between the upper andlower molds 70 and 71. The bonding portion 62b is contacted onto thecavity surface 72a of the upper mold 70. The intermediate connectingportion 62f and the intermediate connecting portion 62g extending fromthe bonding portion 62a are arranged in the cavity 72. The intermediateconnecting portion 62f is supported by a comb-shaped support plate 66extending from a groove 69 formed in the lower mold 71.

The manner of supporting the connection lead 62 by means of thesupporting plate 66 is clearly illustrated in FIG. 25. Each leg 66a ofthe supporting plate 66 is inserted between the adjacent leads of theconnection lead 62. Each lead of the connection lead 62 is depressedtoward the upper mold by the root portion 66b of the support plate 66.As a result, each lead of the connection lead 62 can be properlymaintained to prevent the respective leads from contacting with eachother.

On the other hand, by the depression force (f) depressing the supportingplate 66 toward the upper mold 70, the bonding portions 62a and 62breceive a reacting force (f) directed from the upper mold 70 to thelower mold 71. As a result, the connection lead 62 is maintained withthe appropriate attitude in the cavity 72. Thereafter, in the frame 10following molding, the bonding portions 62a and 62b of the connectionlead 62 are respectively situated to be exposed on the horizontal plane22h of the second stepped portion 22 and the horizontal plane 24h of thefourth stepped portion 24. Therefore, a failure in molding can besuccessfully prevented.

It should be appreciated that when the connection lead 620 is simplyformed into a U-shaped configuration, and since no intermediateconnection portion (the portion corresponding to 62g of FIG. 24) suchthat the depression force (f) of the supporting plate 66 is not present,it becomes difficult to transmit the depression force (f) to the bondingportion 620b in contact with the upper mold 70. Therefore, the force todepress the bonding portion 620b toward the upper mold 70 becomesinsufficient to possibly create a clearance between the bonding portion620b and the upper mold. In such a case, the resin can be injected intothis clearance so that the bonding portion 620b cannot be exposed.Furthermore, it is also possible to cause an inappropriate attitude ofthe bonding portion 620b so that the bonding portion 620b cannot beformed with a regular pitch.

However, by forming the connection lead 62 in the configurations asillustrated in FIGS. 16 and 25, the bonding portion 62b can be properlyformed on the horizontal surface 24h of the fourth stepped portion 24 ofthe frame 10.

Since it is only required to properly apply the depression force (f) ofthe support plate 66 to the connection lead 62, the configuration of theconnecting lead 62 and the position to apply the depression force by thesupporting plate 66 can be modified as shown in FIGS. 28(a)-28(c).

On the other hand, after molding the frame 10, respective frame portions60c, 61c, 62e, 62d, 63e, 63d and 64c of the lead pins 60 and 61, theconnection leads 62, 63, 64 and 65 are cut away for insulating them fromeach other.

Namely, in the above-mentioned process of fabrication of the electronicdevice, the connection leads are arranged on the surface forming acavity of the mold. Subsequently, the comb shaped plate extends towardthe inside of the cavity from the surface forming the cavity in themold. Then, by establishing engagement between the comb shaped supportplate and the metallic lead, the connection lead can be depressed ontothe cavity surface with the depression force of the support plate. Bythis depression force, the connection lead that is bent in a stepwisefashion can be arranged so as to leave no gap with the cavity surfaceand in the proper attitude. Under these conditions, the frame is molded.

Accordingly, the first and second contact portions of the connectionlead are buried while leaving the surfaces exposed on respective steppedportions formed in the frame. As a result, the shown electronic deviceaccording to the invention can eliminate the possibility of anoccurrence of production failure.

Next, another practical embodiment of the electronic device according tothe present invention will be discussed. FIGS. 2 to 4 briefly showanother embodiment of the electronic device according to the presentinvention.

At the side of the frame 10, a capacitor box 15 is formed, as shown inFIG. 2. Capacitors 56 and 57 are disposed within the capacitor box 15 ina horizontal fashion, as shown in FIG. 3. These capacitors 56 and 57cannot be arranged on the first and second circuit boards 50 and 52 inview of the mounting space. By housing the capacitors 56 and 57 thathave relatively large capacitances and large heights within thecapacitor box 15, which is formed at the side of the frame, the overallpackaging density of the electronic device 1 can be improved.

The connection lead 64 connected to the capacitor 56 is buried in theframe 10 by insert molding. The connection lead 64 is formed by bendingthe metal plate illustrated in FIG. 13 into the configurationillustrated in FIG. 14.

The connection lead 64 has a bonding portion 64a exposed on thehorizontal surface 22h of the second stepped portion 22, a terminalportion 64b vertically extending within the capacitor box 15, and aframe portion 64c. The frame portion 64c is cut away after molding theframe 10. The bonding portion 64a is electrically connected to thewiring pattern of the first circuit board 50 by wire bonding. Theterminal portion 64b is connected to the leads 56a and 56b of thecapacitor 56 by way of electric welding.

On the other hand, at the side of the frame 10 opposite the side wherethe connector casing 14 is formed, the connecting lead 62 that is formedby bending the substantially comb-shaped metal plate illustrated in FIG.15 at a substantially right angle to form the configuration illustratedin FIG. 16 (in the configuration defining substantially U-shapedconfiguration with transversely extending portion) is buried in theframe 10 by insert molding. The connection lead 62 has the bondingportion 62a formed at one end, which is exposed on the horizontal plane22h of the second stepped portion 22. The connection lead 62 also has anintermediate portion 62g buried within the frame body. On the otherhand, the bonding portion 62b of the connection lead 62b is exposed onthe horizontal plane 24h of the fourth stepped portion 24. The tip end64c at the other end is extended into a groove 26 formed on thehorizontal plane 21h of the first stepped portion 21.

It should be noted that the frame portion 62d commonly holdingrespective leads extends into the groove 26 immediately after finishingthe molding process. However, the frame portion 62d is then cut away.Similarly, the frame portion 62e is cut away after molding, and by this,respective leads are separated in a mutually insulated fashion. In orderto facilitate cutting away of the frame portions 62d and 62e, a cut linemay be preliminarily provided.

As shown in FIG. 1, the bonding portion 62a of the connection lead 62and the bonding portion 83 of the wiring pattern of the first circuitboard 50 are electrically connected to each other by wire bonding.Similarly, the bonding portion 62b of the connection lead 62 and thebonding portion of the wiring pattern of the second circuit board 52 areelectrically connected by the wire bonding. Therefore, by employing theconnection lead 62, the first and second circuit boards 50 and 52 areelectrically connected.

Furthermore, at the side of the frame where the connection lead 62 isarranged, the connection lead 65 having substantially the sameconfiguration as the connection lead 64 illustrated in FIG. 14 is buriedin the frame 10. The connection lead 65 has the bonding portion 65aexposed on the horizontal plane 22h of the second stepped portion 22,and a terminal portion 65b vertically extending into the capacitor box15. The bonding portion 65a and the wiring pattern of the first circuitboard 50 are electrically connected by the wire bonding. The terminalportion 65b is connected to the lead 57b of the capacitor 57 by way ofelectric welding.

Next, discussion will be provided for the construction of the circuitboard 50 in an electronic device according to the present invention.

On the first circuit board 50, a circuit wiring corresponding to thepower supply circuit 51 illustrated in FIG. 3, is provided. When thefirst circuit board 50 is mounted on the first stepped portion 21, adummy wiring 54 having a projection is formed at a position spaced fromthe inner boundary 21a of the horizontal plane 21h of the first steppedportion as illustrated in FIGS. 5 and 6, by Δ1. On the other hand, atthe inside of the dummy wiring 54, a recessed portion 55, to which nowiring is provided, is formed.

The dummy wiring 54 and the recess 55 function as follows.

When the first circuit board 50 formed on the metal plate 40 is mountedon the horizontal plane 21h of the first stepped portion 21 by theadhesive, the excess amount of adhesive tends to flow across theboundary 21a of the horizontal plane 21h into the first circuit board 50to adhere on the connecting portion 59 of integrated circuits 58 mountedon the first circuit board, or causes abnormal conditions in the bondingcapacity during bonding thereby causing degradation of reliability ofthe bonding. On the other hand, the excess amount of adhesive can adhereon the bonding portions 81 and 83 of the circuit wiring which causesbonding failure.

At this time, as shown in FIG. 17, the dummy wiring 54 formed on thefirst circuit board 50 blocks the flow of adhesive, which caused theproblems set forth above. Namely, the excess amount of adhesive 17 isaccumulated within a small clearance Δ1 between the boundary 21a of thehorizontal plane 21h and the dummy wiring 54. In addition, even when anamount of the adhesive flows over the dummy wiring to enter the firstcircuit board 50, such adhesive can be successfully trapped within therecessed portion 55 so that no adhesive may enter further inside therecessed portion 55. As a result, damage of the elements by the adhesivecan be successfully prevented and a failure of wire bonding will notoccur.

It should be noted that the dummy wiring is a wiring irrespective of theelectric wiring or grounding line.

Next, several practical examples of the third embodiment of theelectronic device according to the present invention will be discussed.

As the first example of the third embodiment, the electronic device, inwhich a plurality of circuit boards mounting electronic circuits arearranged in a multi-board structure, comprises a frame including astepped inner wall having horizontal planes supporting peripheralportions of the circuit boards, vertical planes restricting the positionof the circuit boards in the horizontal direction and extending from thehorizontal planes; the circuit board having a size supported by thehorizontal plane and forming a clearance with respect to the verticalplane, and a projection, projecting toward the clearance for contactingwith the vertical plane or the peripheral edge of the circuit board, isformed on the peripheral edge of the circuit board or the verticalplane.

With such a construction, the circuit board is mounted on the steppedportion formed on the inner side wall of the frame in a stepwisefashion. The stepped portion is formed in a stepwise fashion to providehorizontal and vertical planes. The circuit boards are bonded onto thehorizontal planes by the adhesive. The peripheral edge portion of thecircuit board is arranged on the horizontal plane. The size of thecircuit board is slightly smaller than the size defined by the verticalplane so that a clearance is defined between the peripheral edge of thecircuit board and the vertical plane. At several positions on theperipheral edge of the circuit board, projections projecting into theclearance are formed. The tip end of the projections makes contact withthe vertical plane. As an alternative, several projections projectinginto the clearance are formed on the vertical plane, tip ends of whichmake contact with the peripheral edge of the circuit board.

Accordingly, when the circuit board is arranged on the stepped portionof the frame, between the peripheral edge of the circuit board and thevertical plane, the clearance is formed because of the presence of theprojection. The back side of the peripheral portion of the circuit boardis bonded to the horizontal plane by the adhesive, the excess amount ofadhesive can be trapped within this clearance. Therefore, the excessamount of adhesive will never flow onto the circuit board. Also, aplurality of leads are formed on the frame in the vicinity of thecircuit board for wiring connection with the circuit board. With theshown construction, the adhesive will never adhere on these leads.Accordingly, the adhesive will not adversely effect the electroniccircuit mounted on the circuit board. Also, the adhesive will not adhereon the bonding portion of the lead and thus will never be a cause ofconnection failure.

In the second example of the third embodiment, the electronic device, inwhich a plurality of circuit boards with electronic circuits mountedthereon are arranged in a multi-board structure, has a stepped portionformed in stepwise fashion on the inner wall of the frame, which hashorizontal planes for supporting the peripheral portion of the circuitboard or closure lid of the casing, and grooves formed at the side ofthe inner boundary in the horizontal plane.

In the third and fourth examples of the third embodiment of theelectronic device, in which the circuit boards mounting the electroniccircuits are arranged in a multi-board structure, is provided with astepped portion on the inner wall of the frame, the stepped portion ofwhich being formed in a stepwise fashion with the horizontal planes forsupporting the peripheral portion of the circuit board and the closurelid members of the casing and vertical planes defining a position toarrange the circuit board and the closure lid member of the casing inthe horizontal direction and extending from the horizontal planes, andgrooves formed in the vicinity of the boundary between the horizontalplanes and the vertical planes.

Furthermore, according to the invention, in the electronic device havinga multi-board structure of a plurality of circuit boards mountingelectronic circuits and coated by a gel form coating agent, the innerwall of the frame is formed with stepped portions for restricting theupper surface of the coating agent that coats the circuit board.

Namely, with the above-mentioned construction, the circuit board and theclosure lid are mounted on the stepped portion of the inner wall of theframe formed into a stepwise fashion. The stepped portion is formed intoa stepwise fashion with horizontal planes to which the circuit board andthe closure lid member are bonded by the adhesive. Since the grooves areformed on the horizontal plane at the inside of the boundary withrespect to the space of the frame, the excess amount of adhesiveprovided between the circuit boards or the closure lids and thehorizontal surfaces can be trapped within this groove. As a result, theexcess amount of adhesive will never drip down to the lower circuitboard or so forth.

Also, the stepped portion defined by the horizontal plane and thevertical plane is provided with a groove at the side of the boundarybetween the horizontal plane and the vertical plane. By this, when thecircuit board is bonded onto the horizontal plane by bonding, the excessamount of adhesive is trapped in this groove. Therefore, the excessamount of adhesive will never flow up along the vertical plane.

In addition, since the stepped portion that defines the upper surface ofthe gel form coating agent, is formed on the inner wall of the frame,the coating agent is restricted to the upper surface by the surfacetension thereof and will never leak upward.

Accordingly, the excessive amount of adhesive will not drip down to thelower side circuit board or climb up to the upper side circuit board toadversely effect the electronic circuit thereon. Therefore, anelectrical connection failure otherwise caused by the dripping orclimbing of the adhesive, can be successfully prevented.

Also, the gel form coating agent will not climb to the horizontal planeof the stepped portion for supporting other circuit boards and thus willnever adhere on the connection lead, and a bonding failure or connectionfailure will not occur.

In addition, cracking or degradation of the heat radiation effect duringto the difference of the thermal expansion coefficients and/or theviscosities of the circuit board and the adhesive, can be successfullyprevented.

The fifth example of the third embodiment of the electronic deviceaccording to the invention includes a frame that defines the casing, andhas an inner wall formed into a stepwise configuration that hashorizontal portions in contact the peripheral portion of the wiredsurface of the circuit board and bonded there by the adhesive; the wiredsurface of the circuit board has a dummy wiring with a circuit patternformed inside while maintaining a substantially small clearance relativeto the inner boundary of the contacting region where it makes contactwith the horizontal plane. In addition, a cut out is formed at the sideof the inner boundary of the horizontal portion of the stepped portion.

In the construction set forth above, the wired surface of the circuitboard is bonded with the horizontal plane of the stepped portion formedon the frame at the peripheral portion. At this time, the excess amountof adhesive can flow across the inner boundary of the contacting regionof the circuit board mating with the horizontal plane of the steppedportion into the wired surface of the circuit board.

However, since the circuit board is formed with a dummy circuit and withthe circuit pattern inside while leaving a substantially small clearancerelative to the inner boundary, the excess amount of adhesive can betrapped within the small clearance between the inner boundary and thedummy wiring so that the adhesive is prevented from flowing beyond thedummy wiring. Accordingly, the electronic circuits mounted on thecircuit boards will never be affected by such excess amount of adhesive.Also, in the shown embodiment, the adhesive will never adhere on theconnecting portion to cause a connection failure. In addition,degradation of the heat radiation effect owing to the difference of thethermal expansion coefficients or viscosities between the circuit boardand the adhesive can be prevented.

Furthermore, since the cut out is formed at the inner boundary of thehorizontal plane, a clearance defined by the cut out and the circuitboard may also serve to trap the excess amount of fuel.

Hereafter, the practical embodiments of the foregoing constructions ofthe electronic device will be discussed with reference to the drawings.

The first stepped portion 21 of the frame 10 in FIG. 5 is formed withcut-outs 21b at the inner boundary 21a of the horizontal surface 21h. Asshown, the cut-out 21b can be formed obliquely. As an alternative, thecut-out 21b can be rectangular or essentially U-shaped configurations asillustrated in FIGS. 18(a) and 18(b).

The effect of the cut out is as follows.

When the first circuit board formed on the metal plate 40 is bonded ontothe first stepped portion 21 by the adhesive, the excess amount ofadhesive 17 is accumulated within a space defined by the cut-out 21b,the surface of the first circuit board 50 and the dummy wiring 54. As aresult, the excess amount of adhesive 17 is prevented from flowinginside the first circuit board 50. Therefore, adverse effects of theadhesive to the integrated circuit 58 of the power supply circuit 51 canbe successfully prevented.

On the other hand, the excess amount of adhesive 17 is prevented fromswelling up to the horizontal plane 22h of the second stepped portion22. Therefore, the bonding portion 60b of the lead pin 60, the bondingportion 63a of the connection lead 63, the bonding portion 64a of theconnection lead 64, the bonding portion 62a of the connection lead 62and the bonding portion 65a of the connection lead 65 are maintainedfree of the adhesive 17 so that a wire bonding failure will never occur.

In the third stepped portion 23 of the frame 10 illustrated in FIG. 5,groove 23b is formed at the inner boundary 23a of the horizontal plane23h of the third stepped portion 23. Also, groove 23d is formed at theouter boundary 23c of the horizontal plane 23h. These grooves 23b and23d may be configurations, other than a rectangular configuration suchas a triangular configuration. Also, these grooves may be the sameconfiguration as those illustrated in FIGS. 18(a) and 18(b).

The effect of the grooves 23b and 23d formed in the third steppedportion 23 are as follows.

When the metal plate 43 (as the second metal plate) is bonded onto thehorizontal plane 23h of the third stepped portion 23, the excess amountof adhesive 17 is accumulated within the groove 23b. As a result, theexcess amount of adhesive is prevented from dripping to the horizontalplane 22h of the second stepped portion 22 positioned lower than thehorizontal plane 23h. Therefore, the bonding portion 60b of the lead pin60, the bonding portion 63a of the connection lead 63, the bondingportion 64a of the connection lead 64, the bonding portion 62a of theconnection lead 62 and the bonding portion 65a of the connection lead 65are maintained free of the adhesive so that a wire bonding failure willnever occur.

On the other hand, with the groove 23b, the climbing of the silicon gel16 on the first circuit board 50 to the horizontal plane 23h of thethird stepped portion 23 makes it easy to adhere the adhesive on thehorizontal plane 23h to successfully prevent a bonding failure betweenthe horizontal plane 23h and the metal plate 43.

It should be noted that in order to prevent the silicon gel 16 fromreaching the horizontal plane 23h of the third stepped portion 23, itmay be equally effective to provide a projection on the vertical plane22v of the second stepped portion 22 projecting perpendicular to thevertical plane 22v.

On the other hand, the excess amount of adhesive 17 also accumulates inthe groove 23d. As a result, climbing of the excess amount of adhesive17 along the vertical plane 23v of the third stepped portion can beprevented. Therefore, the adhesive 17 is prevented from adhering to thewiring pattern of the second circuit board 52. Also, the bonding portion61b of the lead pin 61, the bonding portion 63b of the connection lead63 and the bonding portion 62b of the connection lead 62, which arearranged on the horizontal plane 24h of the fourth stepped portion 23,are held free of the adhesive. Therefore, a wire bonding failure willnever occur.

Next, in contrast to the first electronic circuit board 50 contactingwith the first closure lid member 40, when the supporting plate 43supporting the other electronic circuit board, such as the secondelectronic circuit board 52, is made of the metal plate, the metal plate43 is formed to be slightly smaller than the side defined by the outerboundary 23 of the horizontal plane 23h of the third stepped portion 23,as shown in FIGS. 19 and 20. When the metal plate 43 is mounted on thehorizontal plane 23h, a small clearance Δ2 is defined between theperipheral edge of the metal plate 43 and the vertical plane 23v. On theperipheral edge of the metal plate 43, a plurality of outwardlyextending (toward the vertical plane 23v) projections 43a are formed. Onthe other hand, on the vertical plane 23v, a plurality of inwardlyextending (toward the peripheral edge of the metal plate 43) projections23e are formed.

The effect of the projections 43a and 23e are as follows.

The projections 43a and 23e serve to position the metal plate 43relative to the third stepped portion 23 and define the small clearanceΔ2 between the peripheral edge of the metal plate 43 and the verticalplane 23v. With this clearance Δ2, the bonding portion 61b of the leadpin 61, the bonding portion 63b of the connection lead 63, the bondingportion 62b of the connection lead 62 are insulated from the metal plate43. Also, the clearance Δ2 serves to accumulate the excess amount ofbond 17 to successfully prevent the excess amount of bond 17 fromclimbing along the vertical plane 23v. Therefore, the adhesive willnever adhere on the wiring pattern of the second circuit board 52 thatmates with the metal plate 43. Also, the bonding portion 61b of the leadpin 61 and the bonding portion 62b of the connection lead 62 aremaintained free of the adhesive so as not to cause a wire bondingfailure.

Next, discussion will be provided for the fifth stepped portion 25provided in the frame 10 of FIG. 5.

As shown in FIG. 21, the groove 25b is formed at the inner boundary 25aof the horizontal plane 25h of the fifth stepped portion 25. The groove25b can be of any configuration, other than a rectangular configurationas shown such as a triangular configuration. Also, the groove 25b can beof the same or similar configurations to that illustrated in FIGS. 18(a)and 18(b).

The effect of the groove 25b formed in the fifth stepped portion 25 isas follows.

The metal plate 46 is bonded onto the horizontal plate 25h of the fifthstepped portion 25. At this time, the excess amount of adhesive isaccumulated within the groove 25b. As a result, the excess amount ofadhesive will never drip down. Therefore, the bonding portion 61b of thelead pin 61 and the bonding portion 62b of the connection lead 62 can beheld free of the adhesive so that a wire bounding failure will neveroccur. Also, adhesion of the adhesive to the wiring pattern of thesecond circuit board 52 can be successfully prevented.

In addition, with the groove 25b, the climbing of the silicon gel 16from the second circuit board 52 to the horizontal plane 25h of thefifth stepped portion 25 facilitates bonding by the adhesive. Therefore,a bonding failure between the horizontal plane 25h and the metal plate46 can be prevented.

It should be noted that, in order to prevent the silicon gel 16 of thesecond circuit board 53, it is possible to provide a projection on thevertical plane 24v of the fourth stepped portion 24 so that theprojection projects perpendicular to the vertical plane 24v.

Next, the construction of the lead pins 60 and 61 to be employed in theelectronic device according to the present invention will be discussed.

The lead pins 60 and 61 are formed by bending the flat metal platesillustrated in FIGS. 7 and 9 into the bent configurations as illustratedin FIGS. 8 and 10. The pitches of respective leads are widened from theside of the bonding portions 60b and 61b to the side of the pins 60a and61a. With the shown construction, in which the pitches of the leads atthe side of the pins 60a and 61a are set to be relatively wide and thepitches of the leads at the side of the bonding portions 60b and 61b areset to be relatively narrow, the pins can be effectively extended evenwhen the internal space receiving the lead pin is relatively small. Inaddition, the lead pins 60 and 61 are of trapezoidal configuration insection, as shown in FIG. 22. With this sectional configuration, whenthe bonding portions 60b and 61b of the lead pins are buried in theframe in a fashion exposed from the horizontal planes 22h and 24h of thesecond and fourth stepped portions 22 and 24 by insert molding,detachment of these bonding portions 60b and 61b from the horizontalplanes 22h and 24h can be successfully prevented.

Next, the construction of the connection leads 62, 63, 64 and 65 asintermediate members to be employed in the electronic device accordingto the invention will be discussed.

The connection lead 62 is formed by bending the metal plate illustratedin FIG. 15 into the bent configuration illustrated in FIG. 16. Theconnection lead 62 has wider pitches of respective leads at the side ofthe bonding portion 62b than that of the bonding portion 62a. With theshown configuration, electrical connection can be effectivelyestablished without reducing the number of leads between the firstcircuit board having a narrower bonding space and the second circuitboard having a wider bonding space.

On the other hand, the connection lead 63 is formed by bending the flatmetal plate of FIG. 11 into the bend configuration as illustrated inFIG. 12. Similarly, the connection lead 64 is formed by bending the flatmetal plate of FIG. 13 into the bend configuration as illustrated inFIG. 14. Also, the connection lead 65 has a configuration symmetric tothe connection lead 63. With the shown constructions of the connectionleads 64 and 65, electrical connection between the circuit board 50 andthe capacitors 56 and 57 provided in the capacitor box 15 formed in theframe 10 can be established.

On the other hand, the sectional configurations of the connection leads62, 63, 64 and 65 are respectively trapezoidal as shown in FIG. 22.Accordingly, the bonding portions 62a, 63a, 64a and 65a of theconnection leads 62, 63, 64 and 65 can be prevented from detaching fromthe horizontal plane 22h of the second stepped portion 22 when they areburied in the frame 10 by insert molding. Similarly, the bondingportions 62b and 63b of the connection leads 62 and 63 can be preventedfrom detaching from the horizontal plane 24h of the fourth steppedportion 24 when they are buried in the frame 10 by insert molding.

On the other hand, the back side of the frame 10 is constructed asillustrated in FIG. 23. On the back side of the frame 10, grooves 26 and29 are formed. The end 62c and the frame portion 62d of the connectionlead 62 is extended into the groove 26. Similarly, the end 63c and theframe portion 63e of the connection lead 63 is extended into the groove29. When molding of the frame, in which the connection leads 62 and 63are inserted, is completed, the frame portions 62d and 63e of theconnection leads 62 and 63 are cut within these grooves 26 and 29.

Furthermore, at the positions corresponding to the intermediate portion62f (see FIG. 16) connected to the bonding section 62a of the connectionlead 62 and the intermediate portion 60d (see FIG. 8) connected to thebonding portion 60b of the lead pin 60, windows 27 and 28 are formed.Among these, the window 27 is formed for receiving a support plate 66that is adapted to support the connection lead 62 to prevent deformationand positional offset during a production process discussed later. Thesewindows 27 and 28 are also used for assuring that respective leads ofthe connection lead 62 and the lead pin 60 are disposed in the framewithout causing a short during contact, after completion of the molding.

Discussion will be provided for the manner of connection between thecapacitor and the intermediate connection lead 64 as the intermediateconnection member.

The connection lead 64 is formed in the configuration as illustrated inFIG. 26. The terminal portion 64b is formed with a welding region 64d tobe connected with the leads 56a and 56b of the capacitor 56 by electricwelding. The welding region 64d is formed to have a smaller length inthe axial direction (h axis direction) than in the width direction (daxis direction. With such a construction, the contact areas of the leads56a and 56b to the welding region 64d are made smaller to enable aconcentration of the current during the electric welding.

Also, since the leads 56a and 56b are extended through the cut out 64f(FIGS. 29(a)-29(e), the displacement of the leads 56a and 56b from thedesired position upon positioning and welding can be successfullyprevented. Also, the cut-out may also serve to maintain the distancebetween the leads 56a and 56b so that shorting will never be occur evenwhen the electronic device according to the invention experiences severevibration. Furthermore, since the leads 56a and 56b are engaged with thecut-out 64, vibration energy to be transmitted to the welding portionsof the leads 56a and 56b can be effectively absorbed to eliminate thepossibility of a disconnection of the connecting portions.

The welding region 64d and the cut-out 64f may be formed in theconfiguration as illustrated in FIG. 29 so as to obtain effectiveconcentration of the welding current. Similar to that illustrated inFIG. 28, by bending the lead 56a to pass through the cut-out 64f asshown in FIG. 29(d), the displacement of the lead upon positioning andwelding can be successfully prevented. Similarly, even when theelectronic device is applied at a portion experiencing substantialvibration, shorting between the leads will never occur. In addition, asset forth above, since the vibration energy can be successfullyabsorbed, disconnection of the connecting portion will never occur.

For example, when the electronic device is disposed in the enginecompartment of an automotive vehicle, transmission of the vibration tothe terminal portion 64d can be successfully reduced to prevent theconnecting portion from being separated,

As set forth above, the preferred construction of the lead and theintermediate connecting member to be employed in the electronic deviceaccording to the present invention comprises wire form leads, anessentially elongated strip shape of terminal, in which the leads arearranged in a direction parallel to the longitudinal axis of theterminal; the welding region at the tip end of the terminal is formed tohave a length in the longitudinal direction shorter than the length ofthe shorter axis perpendicular to the longitudinal axis. Below thewelding region, the cut-out portion is formed in the terminal.

The longitudinal axis of the terminal and the wire form leads arearranged parallel to each other. The welding region of the terminal isprovided with a smaller length in the longitudinal direction than thewidth direction with the cut-out formed below the welding region.

Therefore, although the wire form leads have a tendency to slip in thewidth direction of the terminal, no substantial problem will occur by aslight offset since the length in the width direction is greater thanthat in the length direction. Also, by shortening the longitudinaldimension of the welding region, the contact area between the weldingregion and the leads can be narrowed to enable a higher concentration ofthe welding current.

Furthermore, the cut-out formed in the terminal contributes to accuratepositioning of the leads relative to the terminal.

In summary, the electronic device according to the present inventionachieves the following advantages.

(1) According to the present invention, the electronic device comprisesthe frame, the metal plate arranged for closing one of the openings ofthe frame; the first electronic circuit handling a relatively largecurrent to generate a relatively large amount of heat is mounted on themetal plate board, and the second electronic circuit handling arelatively smaller current to generate a small amount of heat which ismounted at the intermediate position of the frame parallel to the metalplate.

Therefore, the large amount of heat generated by the first electroniccircuits is radiated externally through the metal plate. On the otherhand, since the amount of heat generated by the second electroniccircuit is small, sufficient heat radiation effect can be obtained evenby radiation of the heat into the internal space of the frame and byheat radiation to the second circuit board and the frame.

(2) According to the invention, the electronic device also comprises thefirst and second circuit boards, first and second lead pins having amulti-pin structure extending from the inside to the outside through theframe and connected with the first and second circuit boards atrespective inner ends, a connecting member maintained at the inside ofthe side wall of the frame at the side opposite the side where the firstand second lead pins are arranged in the stepwise bent fashion, firstconnecting portion arranged and exposed to the horizontal surface of thestepped portion formed in stepwise fashion at the inside of the sidewall of the frame and electrically connected to the connecting portionof the first circuit board and second connecting portion arranged andexposed to the horizontal plane of another stepped portion formed on theside wall and electrically connected to the connecting portion of thesecond circuit board.

Accordingly, by employing the connected leads buried in stepwise bentfashion in the frame of the multi-lead structure, the first and secondcircuit boards arranged in a two stage structure can be easilyconnected. In this case, the number of connection lines can be increasedup to the number determined by the dimension of the device. Also, theexternal input and output of the signals is performed throughspecialized lead pins and an electrical connection between the circuitboards is established by specialized connection leads. Therefore, itbecomes unnecessary to provide the dummy lead pin for connecting betweenthe circuit boards so that lead pins can be effectively used.

(3) According to the present invention, the electronic device furthercomprises an intermediate connecting member held in a stepwise bentcondition in the side wall of the frame, which is so arranged that thehorizontal plane of one of the stepped portions is exposed to the firstconnecting portion and the horizontal plane of another stepped portionis exposed to the second connecting portion, which establishes anelectrical connection with the connecting portion of the second circuitboard.

At one side of the frame, with the intermediate connection lead, i.e.the intermediate connection member buried in the frame, an electricalconnection between the first and second circuit boards can befacilitated. Also, the number of connection lines can be increased up tothe number determined by the dimension of the device.

In the production process of the electronic device as set forth above,when the frame is molded by setting the connection lead as an insert,the connection leads are arranged on the surface forming the cavity ofthe mold. A comb-shaped support plate extended toward inside of thecavity from the surface forming the cavity of the mold so as to engagewith a plurality of metallic leads at the extended portions. When theconnection lead is thus fixed in the cavity, molding of the frame isperformed.

Accordingly, with the depression force on the supporting plate, thestepwise bent connection leads can be firmly fitted onto the cavitysurface of the mold and thus can be arranged in correct attitude. Byperforming molding at this position, the first and second connectingportions of the connection lead can be buried exposing the surface ofthe horizontal planes. As a result, the electronic device according tothe invention can minimize the occurrence of defects.

(4) Also, according to the present invention, the electronic devicecomprises a frame including stepped inner wall having horizontal planessupporting peripheral portions of the circuit boards, vertical planesrestricting the position of the circuit boards in the horizontaldirection and extending from the horizontal planes; the circuit boardhaving a size so as to be supported by the horizontal plane and to forma clearance with respect to the vertical plane, and a projectionprojecting toward the clearance for contacting with the vertical planeor the peripheral edge of the circuit board is formed on the peripheraledge of the circuit board or the vertical plane.

Accordingly, when the circuit board is arranged on the stepped portionof the frame between the peripheral edge of the circuit board and thevertical plane, the clearance is formed because of the presence of theprojection. The back side of the peripheral portion of the circuit boardis bonded to the horizontal plane by the adhesive, the excess amount ofadhesive can be trapped within this clearance, and therefore, the excessamount of adhesive will never flow onto the circuit board. Also, aplurality of leads are formed on the frame in the vicinity of thecircuit board for a wiring connection with the circuit board. With theshown construction, the adhesive will never adhere on these leads, andaccordingly, the adhesive will not adversely effect the electroniccircuit mounted on the circuit board. Also, the adhesive will not adhereto the bonding portion and the lead and thus will never be a cause ofconnection failure.

(5) In the electronic device according to the present invention, theframe has a stepped portion formed in a stepwise fashion on the innerwall of the frame, which has horizontal planes for supporting theperipheral portion of the circuit board or a closure lid of the casing,and grooves formed at the side of the inner boundary in the horizontalplane.

Accordingly, when the circuit board or the closure lid member is bondedon the horizontal plane of the stepped portion, the excess amount ofadhesive accumulates within the groove and will never drip down. As aresult, the adhesive will not adhere to the electronic circuit mountedon the circuit board, the bonding portions of the circuit board or theconnection leads electrically connecting the circuit boards disposed inthe frame. Therefore, adverse effects, wire bonding failure ordegradation of heat radiation effect can be successfully prevented.

Alternatively, according to the invention, the stepped portion on theinner wall of the frame is formed in a stepwise fashion with horizontalplanes for supporting the peripheral portion of the circuit board andthe closure lid members of the casing and vertical planes defining aposition arranging the circuit board and the closure lid member of thecasing in the horizontal direction and extending from the horizontalplanes, and grooves formed in the vicinity of the boundary between thehorizontal planes and the vertical planes.

With the foregoing construction, when the circuit board is bonded ontothe horizontal plane the excess amount of adhesive is trapped in thisgroove. Therefore, the excess amount of adhesive will never flow upalong the vertical plane. As a result, the adhesive will not adhere tothe electronic circuit mounted on the circuit board, the bondingportions of the circuit board or the connection leads electricallyconnecting the circuit boards disposed in the frame. Therefore, adverseeffects, wire bonding failure or degradation of heat radiation effectcan be successfully prevented.

Furthermore, according to the invention, in the electronic device havinga multi-board structure of a plurality of circuit boards mountingelectronic circuits and coated by a gel form coating agent, the innerwall of the frame is formed with stepped portions for restricting theupper surface of the coating agent that coats the circuit board.

Since the stepped portion that defines the upper surface of the gel formcoating agent is formed on the inner wall of the frame, the coatingagent is restricted to the upper surface by the surface tension thereofand will never leak upward. Since the gel form coating agent will notclimb up to the horizontal plane of the stepped portion supporting othercircuit boards thus will never adhere to the connection lead, bondingfailure or connection failure will not occur.

(6) On the other hand, according to the present invention, the frame hasa horizontal portion contacting with the peripheral portion of the wiredsurface of the circuit board and bonded therewith by the adhesive, inwhich the wired surface of the circuit board has a dummy wiring with acircuit pattern formed inside while maintaining a substantially smallclearance relative to the inner boundary of the contacting region whereit makes contact with the horizontal plane. In addition, a cut out isformed at the side of the inner boundary of the horizontal portion ofthe stepped portion.

In the construction set forth above, the excess amount of adhesive canbe trapped within the small clearance between the inner boundary and thedummy wiring so that the adhesive is prevented from flowing beyond thedummy wiring. Accordingly, the electronic circuits mounted on thecircuit boards will never be influenced by such excess amount ofadhesive. Also, in the shown embodiment, the adhesive will never adhereto the connecting portion to cause a connection failure. In addition,cracking and degradation of the heat radiation effect owing to thedifference of the thermal expansion coefficients or viscosities betweenthe circuit board and the adhesive can be prevented.

Furthermore, in the present invention, the electronic device compriseswire form leads, an essentially elongated strip shape of terminal, inwhich the leads are arranged in a direction parallel to the longitudinalaxis of the terminal; the welding region at the tip end of the terminalis formed to have a length in the longitudinal direction shorter thanthe length of the shorter axis perpendicular to the longitudinal axis.The cut-out portion is formed in the terminal below the welding region.

Therefore, although the wire form leads have a tendency to slip in thewidth direction of the terminal, no substantial problem will occur by aslight offset since the length in the width direction is provided to begreater than that in the length direction. Also, by shortening thelongitudinal dimension of the welding region, the contact area betweenthe welding region and the leads can be narrowed to enable a higherconcentration of the welding current.

Furthermore, the cut-out formed in the terminal contributes to accuratepositioning of the leads relative to the terminal.

As shown in FIGS. 30 and 31, the present invention is furthercharacterized in that the gel forming coating agent is separatelyinjected over a surface of the first plate and the second plate,respectively, so as to cover a surface of each circuit means formed onboth plates and then the curing operation is carried out simultaneouslyat the final step of this invention so that each of the gel formingcoating agents, covering over the surface of the respective plates, iscured at the same time.

On the other hand, in the present invention, when the gel formingcoating agent is injected into this frame forming the casing, it isfirst injected into a space formed over the surface of the first circuitmeans provided on the first plate, from an injection aperture providedon one side of the casing and through an under path formed underneathone side surface of the casing.

Further, when the gel forming coating agent is injected into this frameforming the casing, preferably the casing should be inclined at acertain angle in the range of from 0° to 90°, preferably 30° to 45°,with respect to a horizontal plane so as to promulgate the gel formingcoating agent over all the surface of the first plate. After that, thesecond plate having the second circuit means mounted thereon is arrangedover the first plate covered with the gel forming coating agent, andthen the gel forming coating agent is injected over the surface of thesecond plate, and the second circuit means mounted thereon, directlythrough a top aperture of the casing.

In the above-mentioned embodiment, when the curing operation for curingthe gel forming coating agent covering the first plate is carried outfirst, previous to the curing operation for the gel forming coatingagent covering the second plate, vaporized silicon particles aredeposited on a write bonding portion formed on the upper step-likeportion of the casing which deteriorates the wire bonding portion.

On the other hand, in the present invention, since both of the gelforming coating agents are cured simultaneously, such a problem can beovercome and the production cost for making the device of the presentinvention will be lowered. Moreover, in the present invention, thewire-bonding operation for forming the wire-bonded portion inside thesubstrate and the wire-bonding operation for forming the wire-bondedportion between the substrate and the casing are carried outsimultaneously, after the first metallic plate having the first circuitmeans mounted thereon is brought into contact with the casing.

In the above-mentioned embodiment, since the second plate is alsoprovided with a reinforcing material, the wire-bonding operationutilizing ultra sonic wave energy, can be carried out, with applying asuitable amount of ultra sonic wave energy, necessary to form a genuinewire-bonded portion, to the wire-bonding portion.

And further, in the present invention, the connecting operation forforming the connected portion between the substrate and the reinforcingmaterial and the connecting operation for forming the connected portionbetween the casing and the reinforcing material are carried outsubstantially at the same time.

FIG. 32 shows one specific embodiment of the curing operation used inthe present invention. A plurality of electronic devices each includingat least two plates having the gel forming coated agent coated thereonare mounted on a conveyer line in a row and they are sequentially movedinto a furnace having at least one gas exhausting duct. An electronicdevice thus cured inside the furnace, the temperature thereof being setat a predetermined value and for a predetermined period, while theelectronic device is moved through the furnace, is taken out from thefurnace.

FIG. 33 shows another embodiment of the present invention in which aplurality of electronic devices each including at least two plateshaving the gel forming coated agent coated thereon are inserted into athermostat and then the curing operation is carried out inside thethermostat kept at a predetermined temperature and for a predeterminedperiod. Then, when the curing operation is completed, the devices havingthe cured coating agent are simultaneously removed from the thermostat.

In FIGS. 32 and 33, the curing operation is carried out under atemperature of 115° C. to 150° C. for 15 to 40 minutes with the framebeing kept in a flat condition. However, this temperature and curingperiod can be changed depending upon the kind of gel forming coatingagent used, and when the temperature is high the curing period can beshortened. Further, it is preferable to pre-heat the frame up to thetemperature at which the gel forming coating agent is cured.

What is claimed is:
 1. A method for producing an electronic devicehaving circuit boards which mount electronic circuits thereon and whichare arranged in a multi-board structure within a casing, said methodcomprising the steps of:preparing a frame forming said casing; engaginga first plate on which a first circuit is mounted with said frame toform a plate of said frame; arranging a second plate on which a secondcircuit is mounted inside said frame at an intermediate position of saidframe and with an interposing space between said first plate and saidsecond plate; injecting a coating agent into said interposing spacebetween said first and second plates through an injection apertureprovided on a side surface of said frame and at a position between saidfirst plate and said second plate, so as to completely cover said firstcircuit with said coating agent; injecting said coating agent over asurface of said second plate through an aperture provided in said frame,so as to completely cover said second circuit with said coating agent;and simultaneously curing said coating agent covering both said firstand second circuits, when said coating agent has completely covered saidfirst and second circuits.
 2. A method for producing an electronicdevice according to claim 1, wherein said steps of injecting saidcoating agent include inclining said frame by a predetermined angle. 3.A method for producing an electronic device according to claim 1,further comprising the step of:arranging a closure lid on said apertureprovided on said frame, before said step of simultaneously curing saidcoating agent.
 4. A method for producing an electronic device accordingto claim 1, wherein said step of engaging said first plate and said stepof arranging said second plate includes temporarily connecting saidfirst and second plates to said frame by utilizing an adhesive agent,before said step of simultaneously curing said coating agent.
 5. Amethod for producing an electronic device according to claim 1, whereinsaid coating agent is a gel forming coating agent.
 6. A method forproducing an electronic device according to claim 1, wherein said framepreparing step includes molding said frame from a resin.
 7. A method forproducing an electronic device according to claim 2, further comprisingthe steps of:wire-bonding a predetermined area of said first circuit,after said step of engaging said first plate with said frame; andwire-bonding a predetermined area of said second circuit, after saidstep of arranging said second plate in said frame.
 8. A method forproducing an electronic device according to claim 3, wherein said stepof engaging said first plate, and said steps of arranging said secondplate and said closure lid include temporarily connecting said firstplate, said second plate and said closure lid to said frame by utilizingan adhesive agent, and wherein said adhesive agent provided on portionsof each of said first and said second plates and said closure lid, iscured simultaneously.
 9. A method for producing an electronic devicehaving circuit boards which mount electronic circuits thereon and whichare arranged in a multi-board structure within a casing having, at aside surface thereof, a capacitor box, said method comprising the stepsof:preparing a frame forming said casing; engaging a first plate onwhich a first circuit is mounted with said frame to form a plate of saidframe; arranging a second plate on which a second circuit is mountedinside said frame at an intermediate position of said frame and with aninterposing space between said first plate and said second plate;injecting a coating agent into said interposing space between said firstand second plates through an injection aperture on said side surface ofsaid frame between said capacitor box and said interposing space betweensaid first plate and said second plate, so as to completely cover saidfirst circuit with said coating agent; and curing said coating agentafter said coating agent has completely covered said first circuit. 10.A method for producing an electronic device according to claim 9,wherein said step of arranging said closure lid is performed so that itsimultaneously covers both said aperture of said frame and an opening ofsaid capacitor box.
 11. A method for producing an electronic deviceaccording to claim 9, further comprising a step of arranging a closurelid on an aperture provided on a portion of said frame.
 12. A method forproducing an electronic device according to claim 9, wherein said framepreparing step includes the step of molding said frame from a resin. 13.A method for producing an electronic device according to claim 9,wherein said coating agent is a gel forming coating agent.